Both galactose and fucose are incorporated into rhodopsin by isolated rod outer segment preparations. These sugars might provide specific markers to permit the pinching off of new disc membranes or the shedding of old discs with resultant phagocytosis by the pigment epithelium during the course of photoreceptor outer segment renewal. Retinyl phosphate, possibly provided by the pigment epithelium, may act as a carrier of galactose. BIBLIOGRAPHIC REFERENCES: O'Brien, P.J.: Incorporation of mannose into rhodopsin in isolated bovine retina. Exp. Eye Res. 24: 449-458, 1977. Bok, D., Hall, M.O., and O'Brien, P.: The biosynthesis of rhodopsin as studied by membrane renewal in rod outer segments. In Brinkley, B.R. and Porter, K.R. (eds.): International Cell Biology, 1976-1977. New York, Rockefeller University Press (in press).